Fuel-fired water heater with air draft inducer and flue heat exchanger

ABSTRACT

A fuel-fired water heater has a tank which holds a reserve of water to be heated by a burner located in a sealed combustion chamber disposed under a bottom heat transfer wall of the tank. A combustion gas exhaust flue extends vertically through the center of the tank in contact with the water therein. A restrictive baffle is secured inside the gas exhaust flue to retard hot gases rising in the flue from the combustion chamber whereby to increase heat transfer from the hot gases to the water in contact with the exhaust flue. A draft inducing blower is secured in a top end of the exhaust flue above the top wall of the tank. A heat exchanger is in communication with a heat exchange section of the flue above the top end of the exhaust flue to extract further heat from residual hot gases in the exhaust flue.

TECHNICAL FIELD

The present invention relates to a fuel-fired water heater and moreparticularly, but not exclusively, a gas fired water heater providedwith a central flue extending through the tank of the water heater andwherein a baffle is disposed inside the flue to retard the exhaustinghot gases drawn up by a draft inducing blower and wherein the efficiencyof the heat exchange is enhanced by a heat exchanger in a top endsection of the flue to further extract heat exhausting from the top ofthe tank.

BACKGROUND ART

It is well known in the art to provide baffles in the exhaust flue ofhot water heaters, such as domestic hot water heaters, whereby to retardthe hot flue gases escaping from the bottom combustion chamber throughthe flue to obtain better heat exchange with the water being heated inthe tank. It is also known to raise the pressure in the combustionchamber to increase efficiency of water heaters by using a morerestrictive baffle. Reference is made to U.S. Pat. No. 7,513,221 as anexample of these. It is also known to install a draft inducer blower atthe top end of the exhaust flue to increase the efficiency of thefurnace and one such blower is described in U.S. Pat. No. 7,278,823.These blowers pull flue gases through the baffle of the flue and thenpush the flue gases out through exhaust piping to the exterior of thebuilding. However, there is a need to increase further this efficiencyof such water heaters by extracting still more heat from the flue gasesleaving the hot water heater.

SUMMARY OF INVENTION

It is a feature of the present invention to provide a fuel-fired waterheater having improved heat exchange between the flue gases to heat thewater in the tank of the water heater.

Another feature of the present invention is to provide a fuel-firedwater heater having a central flue and wherein the heat exchange betweenthe flue and the water in the tank is increased by using a restrictivebaffle in combination with a draft inducer and wherein residual heat inthe exhaust flue is further recovered, in part, by a heat exchanger incommunication with the exhaust flue above the draft inducer.

According to the above features, from a broad aspect, the presentinvention provides a fuel-fired water heater which comprises a tank forholding a reserve of water to be heated by a burner located in a sealedcombustion chamber disposed under a bottom heat transfer wall of thetank. A combustion gas exhaust flue extends vertically through the tankin contact with water therein. The exhaust flue has a bottom open end incommunication with the sealed combustion chamber through the bottom heattransfer wall. The exhaust flue extends through a top wall of the tank.A restrictive baffle is secured inside the gas exhaust flue to retardhot gases rising in the gas exhaust flue to increase heat transfer fromthe hot gases to the water in contact with the exhaust flue. A draftinducing blower is in communication with a top end of the exhaust flueabove the top wall of the tank to allow for increased efficiency of thebaffle for the transfer of heat from the hot gases. A heat exchanger isin communication with a heat exchange section of the exhaust flue abovethe top and of the exhaust flue to extract further heat from residualhot gases in the exhaust flue.

BRIEF DESCRIPTION OF DRAWINGS

A preferred embodiment of the present invention will now be describedwith reference to the accompanying drawings in which:

FIG. 1 is a perspective fragmented view showing a gas fired water heaterto which is secured at the top end of the gas exhaust flue a draftinducer blower;

FIG. 2 is a perspective view similar to FIG. 1 and showing an additionalheat exchanger coil in communication with the exhaust flue above thedraft inducer;

FIG. 3 is a perspective view similar to FIG. 2 and wherein the heatexchanger is located inside the gas exhaust flue above the draft inducerwhereby to further extract heat from the combustion gases exiting thewater heater;

FIG. 4 is a fragmented perspective view showing a further embodiment ofthe heat exchanger secured to the top end of the water heater about anopen and of the gas exhaust flue; and

FIG. 5 is a fragmented side section view of the heat exchanger deviceillustrated in FIG. 4.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to the drawings and more particularly to FIG. 1, there isshown generally at 10 a gas-fired hot water heater of the domestic type.The hot water heater 10 is provided with a hot water glass-lined innertank 15 provided, at a lower end thereof, with a sealed combustionchamber 11 in which there is mounted a fuel-fired burner 12. The burnermay be an oil or gas burner. A vapor sensor 13 is secured close to thebottom end of the outer casing 14 of the hot water heater in closeproximity to an inlet port 9. The outer casing 14 is spaced outwardly ofthe inner tank 15 and an insulation, not shown, surrounds the inner tankin the space 16 between the inner tank outer wall and the outer casing.This is a conventional domestic hot water heater design. Tank 15 mayalso be a stainless steel inner tank or other suitable tank to heatwater therein.

Water to be heated is admitted in the inner tank 15 close to the bottomwall 17 of the inner tank and the hot water, which is hottest in the topend section of the tank, is retracted therefrom by an outlet pipe, notshown. As hereinshown, a central combustion gas exhaust flue 18 extendsvertically through the inner tank 15 and is in contact with the water tobe heated in the tank. The exhaust flue 18 has a bottom open end 19which extends through the bottom wall 17 and in communication with thesealed combustion chamber and is disposed above the burner 12. Arestrictive baffle 20 is secured in the gas exhaust flue 18 whereby toretard the hot flue gases rising through the restrictive baffle.

A draft inducer 21 is secured at the top end 22 of the gas exhaust flue18 and includes a blower 23 whereby to impart a suction or negativepressure in the flue. The draft inducer permits a more restrictivebaffle design to be used, such as illustrated herein, than a standardone, thus increasing the heat transfer from the hot gases to the watercontained in the tank through the wall 18′ of the gas exhaust flue 18.

The draft inducer 21 may also include a damper 24 that will close thedraft inducer when the burner is not in operation thus stopping the hotair exhausting through the chimney by natural draft effect, thereforeminimizing standby losses and increasing overall efficiency. It ispointed out that because the product of combustion exhausting throughthe chimney have been cooled down, a standard chimney, such as plasticpipes, may be used to vent the water heater gas.

The draft inducer 21 may also include one or more pressure switches toensure that the combustion chamber is properly sealed and that anappropriate draft is established and maintained. The draft inducer canalso work on different voltages such as 12, 24 are 120 volts. Ashereinshown the draft inducer has a low profile design to fit the heightof a standard draft hood 24, as shown in FIG. 2. It is also pointed outthat the present design saves energy by not using house heated air forgas dilution, like any normal power vent.

In order to increase the efficiency of the hot water heater as shown inFIG. 1, there is further provided, as shown in FIGS. 2 and 3, a furtherheat exchanger in communication with a heat exchange section of theexhaust flue 18 above the top end of the draft inducer 21 to extractfurther heat from residual hot gases in the exhaust flue.

As shown in FIG. 2, the heat exchanger 30 is a heat extracting conduitcoil 31 in contact about the heat exchange section 32 of the exhaustflue above the draft inducer 21. The heat extracting conduct coil 31 hasan inlet end 33 in communication with a feed tube 34 which extends inthe inner tank 15 to the lower end 35 of the tank to extract cold watertherefrom. As previously mentioned, cold water from the domestic watersupply is introduced in the lower end 35 of the inner tank by a feedtube 34 and enter the tank at its lower end 36. Accordingly, the waterin the tank is cooler at the bottom than at the top where hot waterpropagates. The heat extracting conduct coil 31 has an outlet end 37which is in communication with a return conduit 38 to discharge heatedwater from the heat extracting conduit coil 31 in an upper section ofthe inner tank 15.

A pump 39 is connected to the outlet end 37 to circulate cold water fromthe open end 36 of the feed tube 34, through the conduit coil 31 andback into the tank through the return conduit 38. Of course, the pump 39may also be connected to the inlet end of the conduit coil to serve thesame purpose. The coil 31 may have flat walls communicating with theflue and the coil windings for better contact with the flue and windingsfor improved heat transfer. With this additional heat exchanger 30 theefficiency of heat transfer between the flue gas and the water in thetank is increased to at least 93%.

Another embodiment of the heat exchanger 40 is illustrated in FIG. 3. Ashereinshown the heat exchanger is a heat extracting coil assemblydisposed inside a heat exchange section 41 of the exhaust flue securedabove the draft inducer 21. The heat extracting coil assembly 40 has aconduit coil 42 provided with an inlet end 43 in communication with thefeed tube 44 which extends to the lower end 35 of the inner casing 15 toextract cooler water therefrom. The heat extracting coil 42 has anoutlet end 45 which is in communication with a return conduit 46 todischarge heated water from the heat extracting conduit coil 42 in anupper section of the inner tank 15. The pump 47, secured to the outletconduct 45, circulates the cold water from the bottom of the inner tankthrough the heat exchanger 40 and back into the top end of the innertank. As hereinshown, the heat extracting coil 42 is secured in a heattransfer module comprised of a series of spaced-apart heat sink fins 48.The fins extract heat from the residual hot gases in the exhaust flue asthe gases flow through the fins and transfer heat to the heat extractingcoil 42. The heat transfer module provides a baffle in the flue abovethe draft inducer and this further improves heat extraction from theflue gases.

It is pointed out that the restrictive baffle 20 provides a combustionefficiency of at least 80% and in combination with the heat exchanger 30or 40 this efficiency is increased to about 93%. Thus, there is provideda higher efficient water heater.

Referring now to FIGS. 4 and 5, there will be described a still furtherembodiment of the heat exchanger, herein heat exchanger 50 constructedin accordance with the present invention. As hereinshown the heatexchanger 50 is comprised of a housing 51 having a heat exchange coil 52supported therein. The housing 51 is a thermal insulated housing havinga thermally insulated circumferential side wall 53 and a top wall 54. Acentral exhaust port 55 is provided in the top wall 54. The housingfurther has a bottom wall 56 also provided with a through bore 57through which an open top end section 58 of the flue 18 exits.

Support means, herein in the form of support brackets 75, are under thebottom wall 56 and sit on the top wall 14′ of the outer casing 14. Athermally insulating sleeve 59 is disposed in frictional contact withthe top end section 58 of the flue 18 above the top wall 14′ of thecasing 14.

As hereinshown, the heat exchange coil 52 is comprised of two or more,herein four, spaced-apart concentric conduit windings 60. The innerconduit winding 60′ has an inlet end connected to a water supply conduit61 in communication with the lower end 35 of the inner tank 15. Theouter conduit winding 60″ is provided with an outlet end which issecured to a return conduit 62 secured to an upper section of the tankto discharge heated water from the heat exchanger coil 52 therein. Apump 63 is secured to the water supply conduit 61 to circulate waterfrom the lower end 35 of the tank, through the heat exchanger coils 52and back into the upper portion of the tank.

As better shown in FIG. 5, the open end 58′ of the open top end section58 of the exhaust flue is disposed in a central through bore 64 formedinside the inner conduit winding 60′. A deflector member 65 is supportedin the central through bore 64 spaced above the top end 58′ of the flue.The deflector member 65 is an inverted casing having a cylindrical sidewall 66 and a top wall 67. The deflector member has an open bottom endwhich is of larger diameter than the diameter of the open top endsection 58 of the flue 18 whereby to define an annular passage 68between the open top end section 58 of the flue, i.e., the cylindricalside wall thereof, for the convection of hot gases drawn into thedeflector member 65 by the draft inducing blowers 25 which is nowsecured about the exhaust port 55. A vent pipe 69 is secured to thedraft inducer to exhaust the hot gases exiting the exhaust port toatmosphere.

As better shown in FIG. 5, the top wall 67 of the deflector member is athermally insulated top wall and it has a concave inner face 67′ tofacilitate the reverse flow, as shown by arrows 70, of the hot gasesexiting the open end 58′ of the exhaust flue. The cylindrical side wall66 of the deflector member is constructed of metal to provide good heatconductivity. The side wall 66 is also disposed in frictional contactwith the inner conduit winding 60′ of the heat exchange coil 52 toprovide heat transfer thereto. The inner conduit winding 60′ may haveits conduit flattened on the side contacting the side wall 66.

As illustrated in FIG. 5, the hot gases that are deflected downwardly,as shown by arrow 70, are directed to the lower end 71 of the housing 51and are drawn upwardly through the concentric conduit windings of thecoil 60 by the draft inducing exhaust blower 25 whereby water pumpedthrough the coil 52 is heated while at the same time cooling the hotexhaust gases exiting the open end 58′ of the flue. As previouslypointed out, because of the high efficiency extraction of heat from thehot gases by the use of the combination of the high efficiencyrestrictive baffle 20 in the flue 18 and the heat exchangers 30, 40 or50, it is possible to use vent pipes formed of plastics material wherebyto exhaust the flue gases into atmosphere at the exterior of a buildingstructure.

It is within the ambit present of the invention to cover any obviousmodifications of the preferred embodiment described herein provided suchmodifications follow within the scope of the appended claims. It is alsopointed out that the heated water from the heat exchangers 30, 40 and 50may be feed to a further heat exchanger to heat air prior to returningthe water to the tank.

1. A fuel-fired water heater comprising a tank for holding a reserve ofwater to be heated by a burner located in a sealed combustion chamberdisposed under a bottom heat transfer wall of said tank, air supplymeans to supply air for said burner, a combustion gas exhaust flueextending vertically through said tank in contact with water therein,said exhaust flue having a bottom open end thereof in communication withsaid sealed combustion chamber through said bottom heat transfer wall,said exhaust flue extending through a top wall of said tank, ahigh-efficiency restrictive baffle secured inside said gas exhaust flueto retard hot gases rising in said gas exhaust flue to increase heattransfer from said hot gases to said water in contact with said exhaustflue, a draft inducing blower in communication with a top end of saidexhaust flue above said top wall of said tank to allow for increasedefficiency of said restrictive baffle for the transfer of heat from saidhot gases, and a heat exchanger in communication with a heat exchangesection of said exhaust flue above said top wall of said tank to extractfurther heat from residual hot gases in said exhaust flue.
 2. Afuel-fired water heater as claimed in claim 1 wherein said heatexchanger is a heat extracting conduit coil in contact about said heatexchange section of said exhaust flue, said heat extracting conduit coilhaving an inlet end in communication with a feed tube extending to alower end of said tank to extract cool water therefrom, said heatextracting conduit coil having an outlet end in communication with areturn conduit to discharge heated water from said heat extractingconduit coil in an upper section of said tank, and a pump secured to oneof said inlet or outlet end of said heat extracting conduit coil tocirculate water therethrough.
 3. A fuel-fired water heater as claimed inclaim 1 wherein said heat exchanger is a heat extracting coil assemblydisposed inside said heat exchange section of said exhaust flue, saidheat extracting coil assembly having a conduit coil having an inlet endin communication with a feed tube extending to a lower end of said tankto extract cool water therefrom, said heat extracting coil having anoutlet end in communication with a return conduit to discharge waterfrom said heat extracting conduit coil in an upper section of said tank,and a pump secured to one of said inlet or outlet end of said heatextracting conduit coil to circulate water therethrough.
 4. A fuel-firedwater heater as claimed in claim 3 wherein said heat extracting coil issecured in a heat transfer module comprised of a series of spaced-apartheat sink fins for extracting heat from said residual hot gases in saidexhaust flue and transferring heat to said heat extracting coil, saidheat transfer module providing a baffle for exhausting flue gases.
 5. Afuel-fired water heater as claimed in claim 1 wherein said heatexchanger comprises a housing having a heat exchanger coil supportedtherein, support means to insulatingly support said housing about anopen top end of said exhaust flue above said top wall of said tank, saidopen top end of said exhaust flue being disposed in a central throughhole formed by said heat exchanger coil, a deflector member supported inan upper portion of said central through bore spaced about said open topend and extending inside an inner surface of said heat exchanger coil,said housing having an exhaust port in a top wall thereof spaced abovesaid central through bore, said draft inducing blower being securedabout said exhaust port, said heat exchanger coil being supported insaid housing spaced above a bottom wall of said housing whereby said hotgases rising in said gas exhaust flue are deflected downwardly by saiddeflector member to be connected towards a lower end of said heatexchanger coil to heat water pumped through said heat exchanger coil,said hot gases being cooled by said heat exchanger coil and exhaustedthrough said exhaust port.
 6. A fuel-fired water heater as claimed inclaim 5 wherein said heat exchanger coil is comprised of two or morespaced-apart concentric conduit windings, said conduit windings havingan inlet end and an outlet end, said inlet and being connected to awater supply conduit in communication with a lower end of said tank toextract cold water therefrom, said outlet end being secured to a returnconduit secured to an upper section of said tank to discharge heatedwater from said heat exchanger coil therein, and a pump secured to oneof said inlet or outlet end to circulate water through said heatexchanger coil.
 7. A fuel-fired water heater as claimed in claim 6wherein a vent pipe is secured to said draft inducer to exhaust said hotgases exiting said exhaust port to atmosphere.
 8. A fuel-fired waterheater as claimed in claim 6 wherein said housing is a thermallyinsulated housing.
 9. A fuel-fired water heater as claimed in claim 5wherein said deflector member is an inverted casing having a cylindricalside wall, a top wall and an open bottom end; said open bottom end beingof larger diameter than the diameter of said exhaust flue to define anannular passage between said cylindrical side wall and said exhaust fluefor the connection of said hot gases.
 10. A fuel-fired water heater asclaimed in claim 9 wherein said top wall of said inverted casing is athermally insulated top wall.
 11. A fuel-fired water heater as claimedin claim 10 wherein said top wall has a concave curvature in an innerface thereof to facilitate a reverse flow of said hot gases exiting saidopen top end of said exhaust flue.
 12. A fuel-fired water heater asclaimed in claim 9 wherein said cylindrical side wall is a heatconducting side wall disposed in frictional contact with an inner one ofsaid concentric conduit windings, said inner one of said concentricconduit windings having a coil section thereof flattened for contactwith their heat conducting side wall.
 13. A fuel-fired water heater asclaimed in claim 1 wherein said petroleum-fired water heater is agas-fired domestic water heater.
 14. A fuel-fired water heater asclaimed in claim 13 wherein said tank is one of an inner glass-linedtank or stainless steel tank or other suitable tank, an outer casingspaced from said inner tank and an insulation disposed between saidinner tank and said outer casing.
 15. A fuel-fired water heater asclaimed in claim 1 wherein there is further provided a damper in saidtop end of said exhaust flue to substantially close said exhaust fluewhen said draft inducer is inoperative.
 16. A fuel-fired water heater asclaimed in claim 1 wherein there is further provided a flammable vaporsensor secured to a bottom and of said water heater to prevent saidburner to be ignited in the presence of flammable vapors.
 17. Afuel-fired water heater as claimed in claim 1 wherein said restrictivebaffle provides a thermal efficiency of at least 80%.
 18. A fuel-firedwater heater as claimed in claim 17 wherein said restrictive baffle incombustion with said heat exchanger increases the efficiency to about93%.